1

Investigation of crosstalk in the readout

structure of the Beamcal

K.Afanaciev

2

Design by Sergej Schuwalow

500 m

coupling

T. Sakurai, K. Tamaru, Simple formulas for Two- and Three-dimensional capacitances

Cinterwire = 0.04 pF/cm

Rwire = 10 /m

out1

out2

Ctrace to pad = 1.9 pF/cm

setup

in1

Cdetector = 2.5pF5 x 5 mm2 x 500μm

Schematics:

Physical:

out1

out2

6000e- (w: 1.5ns, trise=100ps) amp1

amp2

5mm

5mm 50μm KaptonεR = 3.9

trace: 17μm thick, 100 wide, 100 pitch, 15x5mm length

Ccross

out1

Lcross

out1

out2

in1

Simulations in T-Spice

Improved model with charge sensitive amplifiers

simulation result

Out = main channel output

Out2 = crosstalk channel output

Ratio of area under the waveforms is about 1/300. Crosstalk estimate 0.3%

Prototype readout structure

Capton foil with conductive traces+

PCB with pad structure

Readout structure prototype with metal pads bonded to capton readout

Prototype resultsSimple experiment with signalgenerator and scope

100 mV/div

1 V/div

Singnal to crosstalk ratio approx. 100/8I.e. 8% crosstalk @9.5 pF input capacitance

4% crosstalk @19.5 pF input capacitance 1 V/div

100 mV/div

Prototype results

C crossC probe

C probe

InputIn this case it works as a capacitive divider

C cross = C probe * U cross / U in

C cross 0.8 pF

From the geometry C cross 0.7 - 0.95 pF

U in

U cross

To cut the crosstalk we need reasonably high input capacitances of the readout preamplifiers

Scope Ch1

Scope Ch2

Further investigation

“Realistic” crosstalkDynamic range of signals in BeamCal is estimated 1:1000

Even with readout crosstalk of 0.1% large signal frominner pads could generate crosstalk comparable withsignal in outer pads.

Simulations with regard to this “realistic” crosstalk, readoutdesign should be made with detector occupancy in mind

Include new preamplifiers in simulations

Prototype measurements with preamplifiers

Investigate screening by absorber layer

Preamplifier design

Szymon Kulis, Krakow AGH University for Science and TechnologySummer student at DESY Zeuthen

http://www-zeuthen.desy.de/students/2007/doc/SzymonKulis_report.ps

Developed a low noise charge sensitive preamlifier for lab use

Preamplifier design

Low noise. ENC 212 e- + 19.2 e-/pF

Details could be found here

http://www-zeuthen.desy.de/students/2007/doc/SzymonKulis_report.ps

Off the shelf components, reasonably low cost

4 channels per 130x125 mm PCB

OK performance, ability to change output polarity and gain on the fly

Could be used for lab measurements and with prototypes